1. Field of the Invention
The present invention relates to a creasing device which can make a crease on paper, and a post-processing apparatus, as well as to a creasing method, an image forming apparatus and a crease-added printing method.
2. Description of the Related Art
In Japanese Unexamined Patent Publication No. 2003-81529, a post-processing apparatus which can fold paper on which an image is formed in, for example, an accordion shape is disclosed. The post-processing apparatus includes a conveying path along which the paper is fed, a conveying roller for feeding the paper, a folding roller for folding the paper in the accordion shape and, in the event that the paper deviates with respect to the conveying path, a correcting mechanism for correcting an angle of the paper, and a sensor for detecting an extent of the deviation of the paper. The correcting mechanism is provided on the conveying roller or the folding roller.
In the post-processing apparatus, in the event that it is detected by the sensor that the paper is deviating with respect to the conveying path, the correcting mechanism operates an installation angle of the conveying roller or the folding roller. The correction is carried out in a condition in which the conveying roller or the folding roller is gripping the paper to correct the deviating paper so as to be straight with respect to the conveying path.
In the U.S. Pat. No. 6,905,118, a post-processing apparatus is disclosed, which is configured in such a way that, after causing the paper to pass through a nipping unit of a pair of folding rollers and making a crease, furthermore, the crease is sharpened by applying pressure to the crease portion in a fold reinforcing roller 400.
However, with the post-processing apparatus described in the Japanese Unexamined Patent Publication No. 2003-81529, as a structure which causes the conveying roller or the folding roller to rotate is adopted, there has been a possibility that a structure of the correcting mechanism becomes large, and also that the post-processing apparatus as a whole becomes large. Also, as the paper is caused to rotate in a condition in which it is held down by a roller, it is sufficient that the paper rotates correctly together with the roller, but there has been a possibility that, in a case in which the paper slips on the roller, and the rotation of the paper is not carried out sufficiently, correction cannot be done correctly. Furthermore, in a case of folding a plurality of sheets of paper by means of the roller, as the crease becomes indistinct, there has been a possibility that an appearance deteriorates when finished. With the post-processing apparatus described in the U.S. Pat. No. 6,905,118, the fold reinforcing roller being necessary, there has been a problem that a structure becomes complex.